Role of diffusion zone structure in the hot corrosion of aluminide coatings on nickel-based superalloys

Abstract Evidence from 900 °C hot corrosion burner rig studies of aluminide-coated nickel-based superalloys demonstrates that sulfidation proceeds relatively rapidly through the additive layer. This is followed by much slower penetration through the diffusion zone if it includes closely spaced acicular phases as is typical in the as-coated condition. However, aging at 1100 °C causes transformation of these closely spaced phases to widely separated blocky carbides with a concurrent drastic decrease in chromium content of the diffusion zone matrix. Once this transformation has occurred, sulfidation through the diffusion zone also can proceed very rapidly and the total hot corrosion life of the coating is severely reduced. The rate of these changes in the diffusion zone is strongly dependent on the identity of the substrate alloy.